This invention relates to a safety device for pattern selection in zigzag sewing machines.
In conventional zigzag sewing machines a needle bar is likely to be oscillated or jogged in a lateral direction when a machine operator manually changes the pattern selecting operation in order to form a desired stitch pattern. The needle is, therefore, subjected to damage, when it is in a penetrated state, that is, it is passing through a needle aperture for zigzag stitching formed in the throat plate during the progress of the pattern selecting operation, because the needle is laterally jogged while it is in close abutment with the edge of the needle aperture.
One of the known devices proposed for solving the problem a cam follower, which is to move for tracking the shape of a pattern cam, is constructed such that its movement is to be transmitted to a needle bar gate by way of a link that is pivoted to the same for normally oscillating in a body with the needle bar gate under the action of a spring; and a stopper is disposed for defining the limit of the jogging of the needle bar. So the lateral shifting of the needle can be prevented, after the needle bar has been laterally shifted to abut the stopper for the pattern selecting operation, because only the link can be then rotated against the spring force. In the event of a pattern selecting operation with such a device, while the needle is in a penetrated state through a thin work fabric pressed on the throat plate by the pressure foot, the work fabric can still be subjected to a damage due to the movement of the needle before the needle bar completely contacts the stopper, because the spring force is greater than the shifting resistance acted on the needle because of existence of the work fabric.
Another further improved device is known as, for example, U.S. Pat. No. 3,820,485. In this device a separable clutch means is disposed between the needle bar and the needle reciprocating mechanism, and a clutch separating mechanism is attached thereto wherein the clutch means can be separated before a cam follower is thrown out of the cam tracking relation in response to the initial movement of a cam follower retracting mechanism. With this arrangement the needle is released from the endwise reciprocating movement mechanism and lifted free above the work fabric by a lifting spring prior to cam follower throw-out. An independent pattern cam selecting means separated from the cam follower retracting mechanism is operated for transferring the cam follower from one pattern cam to another after it has been released from the cam tracking relation. So it is necessary in this device to separately operate a manual handling of the needle elevation and the cam follower releasing as well as a pattern cam selecting operation. Further the device disclosed in the patent needs another special mechanism for making the clutch mechanism between the needle bar and the needle reciprocating mechanism engaged in response to the re-starting of the sewing operation thereafter.